1. Field of the Invention
The present invention relates to method and apparatus for scrubbing either face or both faces of a substrate with a cylindrical brush while chucking only the periphery of the substrate,
2. Description of the Prior Art
Recently, semiconductor devices have been evolved from very large scale integration (VLSI) into ultra large scale integration (ULSI). On a surface of a semiconductor substrate, very minute circuits are densely formed using a precision photolithographic technique. In the production process, microscopic dust particles adhering on the surface of the semiconductor substrate will result in defective semiconductor circuits and reduce the production yield. The production cost steeply rises, as the degree of integration of semiconductor devices increases. Therefore, an improvement in the production yield will largely contribute to the cost reduction, and the removal of dust particles is a very important subject.
At the production site of semiconductor devices, although the cleaning of the front face of a semiconductor substrate on which microcircuits are formed is strictly controlled, control on the cleaning of the back face is not so strict at present. During the production processes, the back face of the semiconductor substrate is brought into contact with suction bases of equipment and handling devices, and becomes contaminated. The contamination of the back face is found to be one of the causes of the contamination of the front face.
Though sufficient cleaning of the back face of the semiconductor substrate has recently been added to the production process, there still exist problems as follows:
(1) Since microcircuits are densely formed on the front face of a semiconductor substrate as previously mentioned, the substrate cannot be supported at the front face thereof for the scrubbing of the back face thereof. Accordingly, the semiconductor substrate has to be supported by chucking the periphery of the substrate with a chuck jaw without supporting a central portion of the front face of the substrate for the scrubbing of the back face. However, since a chuck jaw for chucking the periphery of the substrate slightly projects outwardly of the scrub face of the substrate, a disk brush as shown in FIG. 21 which has a small scrubbing area and hence is of an insufficient scrubbing ability is conventionally used for the scrubbing.
(2) When the back face of the semiconductor substrate is scrubbed with a scrubbing means such as a brush with its periphery being chucked by the chuck jaw as described above, the thin semiconductor substrate is warped by the contact pressure of the brush, so that a central portion of the substrate cannot be sufficiently scrubbed.
(3) Since the chuck jaw projects outwardly of the scrub surface of the semiconductor substrate as described above, peripheral portions of the substrate adjacent the projections of the chuck jaw cannot be sufficiently scrubbed, and some part of the scrub surface remains unscrubbed.
Another problem associated with the production of semiconductor devices is dust particles suspended in the air. Although a production apparatus for semiconductor devices which is related to the present invention is used in a clean room and the amount of dust particles suspended in the air is significantly reduced, there exists a very small amount of suspended dust particles. After the scrubbing of the substrate, these dust particles will adhere onto the surfaces of the substrate charged by static electricity, and the scrubbed surface of the substrate will become contaminated.
In view of the problems associated with the prior art, it is an object of the present invention to provide method and apparatus for scrubbing a substrate which present an enhanced scrubbing ability.
It is another object of the present invention to provide method and apparatus for scrubbing a substrate which prevent a central portion of the semiconductor substrate from being warped by the contact pressure of a brush during the scrubbing operation so as to sufficiently scrub even the central portion.
It is still another object of the present invention to provide method and apparatus for scrubbing a substrate which are capable of scrubbing even peripheral portions of the substrate lying very close to the projections of a chuck jaw for chucking the substrate.
It is a further object of the present invention to provide method and apparatus for scrubbing a substrate which prevent suspended dust particles from adhering onto the substrate by removing electrostatic charge after the scrubbing of the substrate.